1. Technical Field
The present invention relates to the field of metrology, and more particularly, to characterization of metrology targets.
2. Discussion of Related Art
Metrology measurements are very accurate measurements of metrology targets produced on wafers, used to identify and quantify errors and inaccuracy in semiconductor devices. Various methods are used to measure overlay (OVL) between produced layers and various algorithms are used to estimate errors and inaccuracies of the production process and of the metrology measurements themselves. Examples include regression methods based on maximum OVL values, optimization of the weighted OVL calculations, optical methods, noise reduction methods, and recipe optimization.
Exemplary approaches, which are incorporated herein by reference in their entirety, are taught by WIPO Publication No. 2013092106, disclosing producing an elaborate sampling plan having sub-sampling plans which are constrained to a predetermined fixed number of measurement points and is used to control an inspection apparatus; U.S. Pat. No. 8,525,993 disclosing the use of asymmetry metrology that uses the off-diagonal elements of a Mueller matrix calculated using a rigorous electromagnetic model; and Raymond, C. J. 2011, “Improved overlay control using robust outlier removal methods”, Proc. SPIE 7971, Metrology, Inspection, and Process Control for Microlithography XXV, 79711 G, disclosing regression based outlier removal methods.